The Central Government shall by order in writing, apportion the quantity of sugar fixed from time to time for purposes of export under section 4 among the owners in proportion to the quantity of sugar produced, or likely to be produced, by them respectively during the season referred to in sub-section (2) of section 4, and such order shall be communicated to each of the owners, and the quantity so apportioned shall be deemed to be the export quota for the factory of that owner